Thermal stability of C-doped GaAs/AlAs DBR structures

Thermal stability of heavily carbon-doped and undoped DBRs has been investigated by reflectivity measurements and Raman spectroscopy. These analytical techniques are used to study the effect of heavy C-doping on Al–Ga interdiffusion during subsequent high-temperature anneals. Reflectivity spectra around the DBR stop-band wavelength clearly show that the growth-rate is reduced due to etching associated with the CBr4 precursor used, but they also indicate that no Al–Ga interdiffusion that could significantly degrade the DBR performance takes place for any samples during annealing. The results are supported by Raman spectra, which indicate the positions of the LO and LOPC modes do not change when the DBRs are annealed, whether the DBRs are doped or not. Simulations of Al–Ga interdiffusion at GaAs/AlAs DBR interfaces indicates that intermixing up to ∼15nm on either side of each interface will not affect the reflectivity of the DBR stack significantly. The observed small changes in the stop-band central wavelength and peak reflectivity due to annealing is most likely a consequence of increased surface roughness resulted from annealing.